1. Field of the Invention
The present invention relates to a viewfinder apparatus for a camera and, more particularly, to a viewfinder apparatus for a camera including a viewfinder optical system independent of a photographic optical system.
2. Related Art Statement
In a camera having a viewfinder optical system that is independent of a photographic optical system, it is known that a difference in the optical axis between the photographic optical system and the viewfinder optical system brings about a difference (hereinafter called a parallax) in the field of view between these two optical systems.
The parallax varies depending on the distance of the object, that is to be photographed, from the camera. In addition, when the photographic optical system is of a zoom type, the parallax also varies with a focal length thereof.
Such a parallax is conspicuous particularly for short range photography. In order to allow a user to recognize a correct field of vision, visual field correction (parallax correction) is preferably performed so as to match a photographic range with a range of a viewfinder field as much as possible.
In order to provide the parallax correction in the viewfinder optical system, a device has been proposed, in which a field-correcting frame is positioned in close proximity to an image-forming surface of the viewfinder optical system, and is further moved in a direction vertical to the optical axis of the viewfinder optical system, thereby allowing the user to appreciate the photographic range.
As one example of the above, a device for detecting an object distance and then correcting the parallax in a non-staged manner in accordance with such object distance information is described in published Japanese Patent Application Laid-Open No. (Hei) 8-304884.
More specifically, in such a parallax-correcting apparatus as taught in the above publication, a correction quantity-calculating means calculates a correction amount of the parallax on the basis of information on a focal length of the photographic optical system and information on the distance of the object being photographed. Then, the field-correcting frame disposed adjacent to the image-forming surface of the viewfinder optical system is moved in the direction normal to the optical axis of the viewfinder optical system in response to a correction signal that is fed from the correction quantity-calculating means. As a result, the parallax is corrected in a non-staged fashion. Such parallax correction makes it possible to provide the user with a proper viewfinder field at any photographic distance.
However, as given in the above publication, the field-correcting frame is designed to merely move in the direction normal to the optical axis of the viewfinder optical system. This causes an inconvenience in that the field-correcting frame is deviated from the normally curvilinear-shaped image-forming surface of the viewfinder optical system at certain positions during movement, which results in the field-correcting frame being viewed differently.
More specifically, a position at which an image is formed is slightly varied in the direction of the optical axis in a range between a central portion of a field image and its surrounding portion, which field image is formed by means of an objective optical system of the viewfinder optical system. As a result, a diopter is found to be varied in the range between the center of the field image and its peripheral portion when the viewfinder is visually observed. Consequently, when the field frame and the field-correcting frame are merely positioned at a surface vertical to the optical axis, or alternatively are merely driven along such a vertical surface, the field image formed by means of the objective optical system, the field frame, and the field-correcting frame is visually observed at different diopters, depending upon positions in the direction of the optical axis.
In view of the above, an object of the present invention is to provide a viewfinder apparatus for a camera, designed to allow a visual field of a viewfinder optical system, a field frame, and a field-correcting frame to be invariably viewed.
In brief, one aspect of the present invention provides a viewfinder apparatus for a camera including a viewfinder optical system independent of a photographic optical system, comprising: a correction amount-calculating means for calculating a correction amount of parallax between the viewfinder optical system and the photographic optical system on the basis of information concerning at least one of a focal length of the photographic optical system and an object""s distance; a field frame for defining a reference visual field of the viewfinder optical system; a field-correcting frame for correcting the visual field defined by the field frame; and a field variable mechanism for permitting the field-correcting frame to be driven both in a direction vertical to an optical axis of the viewfinder optical system and in a direction of the optical axis of the viewfinder optical system in accordance with the correction amount of parallax calculated by the correction amount-calculating means.
Another aspect of the present invention provides a viewfinder apparatus for a camera, comprising: a viewfinder optical system separate from a photographic optical system, which is for photographing an image of an object; a field-correcting frame for correcting a parallax between the photographic optical system and the viewfinder optical system; a first driving mechanism for driving the field-correcting frame in a direction substantially vertical to an optical axis of the viewfinder optical system; and, a second driving mechanism for driving the field-correcting frame in a direction of the optical axis of the viewfinder optical system.
Yet another aspect of the present invention provides a viewfinder apparatus for a camera, comprising: a viewfinder optical system, through which an object can be observed visually; and a display member movable both in a direction substantially vertical to an optical axis of the viewfinder optical system and in a direction of the optical axis of the viewfinder optical system, the display member being inserted into a visual field of the viewfinder apparatus, thereby allowing the display member to be visually observed.
A further aspect of the present invention provides a viewfinder apparatus for a camera, comprising: a viewfinder optical system for visually observing an image of an object; a field frame for defining a field range of the viewfinder apparatus; and a field-correcting frame for changing the field range defined by the field frame, wherein the field-correcting frame is visually observed at an invariable diopter when the field range is changed.
These object and advantages of the present invention will become further apparent from the detailed explanation.